Method and device for detecting a clutch-bite point

ABSTRACT

Disclosed is a method for detecting a clutch bite-point of a clutch that is connected to a driving motor. A rotational speed of the driving motor and the wheel rotational speed values of the wheels driven by the driving motor are determined. The invention further relates to a device for implementing the method. As the exact clutch bite-point is required as a release criterion for an automatic release operation of an electric parking brake in a motor vehicle, a transmission ratio (f) is determined, which is produced from a quotient of the wheel rotational speed values (v wheel ) and the rotational speed (n) of the driving motor, and that the clutch bite-point is established when the transmission ratio (f) and the rotational speed (n) of the driving motor have a local minimum.

The present invention relates to a method for detecting a clutch bite-point of a clutch that is connected to a driving motor, wherein the rotational speed of the driving motor and the wheel rotational speed values of the wheels driven by the driving motor are determined. The invention further relates to a device for implementing the method.

The exact clutch bite-point is required, for example, as a release criterion for an automatic release operation of an electric parking brake in a motor vehicle. However, the problem is encountered that each clutch is subject to wear, which changes the position of the bite-point.

DE 10 2005 011 032 A1 discloses a method for detecting the point of time of engagement of a clutch that is connected to a driving motor, when a check is made as to whether a torque provided by a driving motor is within a predetermined range and when clutch engagement is detected as soon as a rate of change of the rotational speed falls below a predetermined first threshold value. In the prior art method, the torque provided by the driving motor is required as an input variable, the torque being different in individual internal combustion engines. The torque provided by the driving motor is not measured directly, but is calculated from the rate of injection, the rotational speed of the engine, air quantity, etc. Therefore, the torque is not always available in a sufficient quantity, as is the case after a cold start of the internal combustion engine, for example.

In view of the above, an object of the invention is to improve upon a method in such a way that the clutch bite-point is determined in a reliable manner with a higher rate of precision.

According to the method, this object is achieved in that a transmission ratio is determined, which is produced from a quotient of the wheel rotational speed values and the rotational speed of the driving motor, and in that the clutch bite-point is established when the transmission ratio and the rotational speed of the driving motor have a local minimum. The required rotational speed of the driving motor and the wheel rotational speed values are available with higher precision than the value for the torque of the driving motor, since they are sensed directly by sensors. The effort of application is considerably lower for different internal combustion engines, since the method of the invention does not require the torque that is different for each internal combustion engine.

It is arranged that a clutch pedal travel sensor senses the position of a clutch pedal and that the position of the clutch pedal at the clutch bite-point is saved.

In a particularly favorable improvement, the position of the accelerator pedal is sensed, and the detection of the clutch bite-point is performed exclusively when the accelerator pedal is not applied.

In this respect, the wheel rotational speed values are determined by means of wheel rotational speed sensors, and the accelerator pedal position is determined by means of an accelerator pedal travel sensor.

In a particularly favorable improvement of the method of the invention, the position of the clutch pedal, which corresponds to the clutch bite-point, is used as a criterion for the automatic release of an electric parking brake in a motor vehicle.

The object is achieved in addition in that a means is provided determining a transmission ratio, which is produced from a quotient of the wheel rotational speed values and the rotational speed of the driving motor, and detecting the clutch bite-point when the transmission ratio and the rotational speed of the driving motor have a local minimum.

There is provision of a clutch pedal travel sensor for determining the clutch pedal position, wheel rotational speed sensors for determining the wheel rotational speed values, and an accelerator pedal travel sensor for determining the accelerator pedal position.

The invention will be explained in detail in the following by way of an embodiment making reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic circuit diagram of a hydraulic brake system including an electromechanical unit for executing parking brake operations and on which the method of the invention can be implemented;

FIG. 2 shows a graph illustrating a comparison between the signals of an accelerator pedal travel sensor, the signals of a clutch pedal travel sensor, a transmission ratio, a rotational speed of the driving motor, a torque of the driving motor, and wheel rotational speed values during travel of a motor vehicle.

FIG. 1 represents a circuit diagram of a hydraulic brake system. The hydraulic brake system is equipped with wheel brakes 2 on a first axle, the front axle, which can be pressurized by way of a hydraulic line 9 during service brake operations. To check the desired braking deceleration and realize anti-lock control (ABS) as well as to detect the vehicle speed, wheel rotational speed sensors 12 are associated with the wheels of the front axle whose output signals are sent to an electronic control and regulation unit (ECU) 5. The electronic control and regulation unit 5 is associated with the service brake system. On a second axle, the rear axle, there is also provision of wheel brakes 3, which can be pressurized by way of a second hydraulic line 10 during service brake operations. The rotational speeds of the wheels of the rear axle are determined by using wheel rotational speed sensors 13 and are sent to the above-mentioned electronic control and regulation unit 5. Further, the wheels of the rear axle include an electromechanically operable parking brake in addition to the wheel brakes 3 for service brake operations. The electromechanically operable parking brake comprises two lockable brake devices 4, which, in the capacity of drum brakes 4, are designed with each one spreading lock (not shown). The mentioned spreading lock is operable by an electromechanical adjusting unit 1 by means of a cable pull 11, whereupon the drum brakes 4 are applied. A parking brake operation is executed after the operator has actuated an operating element 7. As this occurs, the output signals of the operating element 7 are sent to an electronic control unit (ECU) 6 associated with the electromechanical parking brake, said ECU correspondingly actuating the above-mentioned electromechanical adjusting unit 1. The above-mentioned electronic control unit 6 and the electronic control and regulation unit 5 associated with the service brake system communicate with each other by way of a data line 8 that can be configured as a CAN connection, for example.

FIG. 1 additionally represents a clutch pedal 14, a service brake pedal 15, and an accelerator pedal 16 as well as a clutch pedal travel sensor 18 that determines the clutch pedal travel. The purpose of the mentioned sensors will be explained in detail in the following.

As has been mentioned already by way of introduction, the exact clutch bite-point is required as a release criterion for an automatic release operation of the electromechanically operable parking brake. After starting of the motor vehicle has been detected, the control unit 6 associated with the parking brake activates the adjusting unit 1 in the sense of a release operation of the parking brake. To detect a starting maneuver, it is initially checked, whether the ignition of the motor vehicle is activated. If this is the case, it is assumed that the motor vehicle shall be moved. For this purpose, an additional check is made, whether the driving motor is in the operating mode. It is found out by evaluation of the signals of the clutch pedal travel sensor 18, whether the operator has depressed the clutch pedal. If the operator releases the clutch pedal 14 from the above-mentioned depressed position, a starting maneuver of the motor vehicle is identified, and the control unit 6 mentioned with respect to FIG. 1 actuates the adjusting unit 1 in the sense of a release operation of the parking brake. As every clutch is subject to wear, the position of the clutch bite-point will change.

The method of the invention for detecting the clutch bite-point is explained in more detail in the following by way of FIG. 2. FIG. 2 illustrates the time variation of some measured variables when downshifting the manual transmission. The time variation shown in the top in FIG. 2 represents the position g of the accelerator pedal 16 and is designated by reference numeral 20. The accelerator pedal position g can assume values between 0% and 100%. As the variation 20 shows, the accelerator pedal 16 is not applied during the detection of the clutch bite-point, since only gear shifts can be evaluated during which the operator does not step on the gas at the clutch bite-point.

The time variation designated by reference numeral 21 represents the position of the clutch pedal 14. The clutch pedal position s can likewise adopt values between 0% and 100%, and the position S_(bite) of the clutch pedal 14 at the clutch bite-point is saved.

To detect the clutch bite-point, a transmission ratio f is determined, which is produced from a quotient of the wheel rotational speed values v_(wheel) and the rotational speed of the driving motor and is designated by reference numeral 22 in FIG. 2. The variation of the mentioned rotational speed n of the driving motor is designated by reference numeral 23, while reference numeral 24 is assigned to the variation of the wheel rotational speed values v_(wheel). It can be seen in the variation 24 that the wheel rotational speed values v_(wheel) lower, i.e. that the speed of the motor vehicle reduces. In the embodiment described, the detection of the clutch bite-point is performed during deceleration of the motor vehicle in the downshifting maneuver.

The operator applies the clutch pedal during gearshift, that means the operator moves the clutch pedal 14 from the non-applied position into an almost fully applied position, as is illustrated in the positions 25 and 26. When the clutch is engaged again after the gearshift in the downshifting maneuver, the torque transmitted by the clutch will speed up the driving motor. The rotational speed n of the driving motor and the transmission ratio f will rise, as becomes apparent from positions 27 to 30. The clutch pedal position S_(bite), at which the rotational speed n and the transmission ratio f, respectively, begin to rise, is saved as the bite-point, that means when the transmission ratio f and the rotational speed n of the driving motor have a local minimum. The total ratio stabilizes itself after clutch engagement at a higher level than before the gearshift. The clutch bite-point is detected by way of rise of the rotational speed n of the driving motor during downshifting.

The values of rotational speed n of the driving motor and wheel rotational speed values v_(wheel) required for the method of the invention are at disposal with a high rate of precision, since they are directly sensed by means of sensors. This allows detecting the clutch bite-point also in a precise fashion. The effort of application of the method at topic to different motor vehicle models is comparatively low.

The method of the invention does not have to be limited to the downshifting maneuver. When the operator disengages the clutch for a very long time in an upshifting maneuver, the driving motor will adjust itself at the level of an idling speed and accelerates when engaging the clutch without depression of the accelerator pedal 16. It is this way possible to extend the scope of application. 

1-8. (canceled)
 9. A method for detecting a clutch bite-point of a clutch that is connected to a driving motor, the method comprising: determining rotational speed (n) of a driving motor; determining wheel rotational speed values (v_(wheel)) of wheels driven by the driving motor; determining a transmission ratio (f), wherein the transmission ratio is determined from a quotient of the wheel rotational speed values (v_(wheel)) and the rotational speed (n) of the driving motor; and establishing a clutch bite-point the transmission ratio (f) and the rotational speed (n) of the driving motor have a local minimum.
 10. The method of claim 9, wherein a clutch pedal travel sensor (18) senses the position of a clutch pedal (14), and in that the position of the clutch pedal (14) at the clutch bite-point is saved.
 11. The method of claim 9, wherein a position of an accelerator pedal (16) is sensed, and the detection of the clutch bite-point is performed exclusively when the accelerator pedal (16) is not applied.
 12. The method of claim 10, wherein the accelerator pedal position is determined by means of an accelerator pedal travel sensor.
 13. The method of claim 9, wherein the wheel rotational speed values (v_(wheel)) are determined by means of wheel rotational speed sensors (12, 13).
 14. The method of claim 9, wherein the position of the clutch pedal (18), which corresponds to the clutch bite-point, is used as a criterion for the automatic release of an electric parking brake in a motor vehicle.
 15. A device for detecting a clutch bite-point of a clutch that is connected to a driving motor, the device comprising: a device for determining rotational speed (n) of the driving motor and wheel rotational speed values (v_(wheel)) of wheels driven by the driving motor; a device for determining a transmission ratio (f), which is produced from a quotient of the wheel rotational speed values (f_(wheel)) and the rotational speed (n) of the driving motor, and detecting the clutch bite-point when the transmission ratio (f) and the rotational speed (n) of the driving motor have a local minimum.
 16. The device of claim 15, further comprising a clutch pedal travel sensor (18) for determining the clutch pedal position, wheel rotational speed sensors (12, 13) for determining the wheel rotational speed values, and an accelerator pedal travel sensor for determining the accelerator pedal position. 